That is strange, because when Scapa mission is available, there is a lot of war ships activity around...and not one or two destroyers!
Destroyers are everywhere as time goes on, and very often i encounter them even in open sea. Rarely alone, often by pairs, sometimes few pairs together. Probably sub hunting...
About ship ID book, if you can call it by pressing E, you should see all info needed inside (keel depth, max speed etc) and of course all nationalities owned.
If not, then your install is messed up somewhere...
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